ASoC: dt-bindings: rockchip: Document reset property for i2s

This patch documents reset property for i2s.

Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1629950562-14281-2-git-send-email-sugar.zhang@rock-chips.com


Signed-off-by: Mark Brown <broonie@kernel.org>